1. Field of the Invention
This invention relates to a process and apparatus for peeling a protective film from an exposed photoresist coating on a printed circuit board, which peeling begins at one corner of the protective film and terminates at the diagonally opposite corner.
2. Description of the Prior Art
It is known that such protective films can be peeled off by hand. For this purpose a knife or fingernail is used to detach the protective film at one corner from the underlying photoresist coating, the triangular corner portion which has been separated is gripped with two fingers and the protective film is then peeled off entirely. But that practice often results in damage to the photoresist coating by the knife edge or fingernail and may result in a tearing or cutting into the protective film, which is notch-sensitive, so that the film may be torn or may even be torn off as it is peeled off.
Published German Application No. 33 39 723 discloses an apparatus for detaching and peeling off the protective film in that adhesive tapes are stuck to the protective film and are used to peel off the film from one corner to the diagonally opposite corner. In the known apparatus the application of the adhesive tapes and the peeling of the protective film are performed as the printed circuit board is supported in a horizontal orientation and advanced by a horizontal conveyor, which constitutes a roller conveyor. A disadvantage of the known apparatus resides in that the adhesive tapes may detach from the protective film as the latter is peeled off so that the sequence of operations may be disturbed. Such disturbances are not tolerable in a substantially automated production line.
From Published German Application No. 27 47 265 it is known to peel off a protective film from a photopolymer which has been laminated to a substrate material. An adhesive tape fixed by means of rollers to the protective film is used to peel off the protective film. That operation is not reliable and may give rise to disturbances in a continuous operation.